Cyanine dyes have been widely used for labeling ligands or biomolecules for a variety of applications such as DNA sequencing. (See, for example, U.S. Pat. No. 5,571,388 for exemplary methods of identifying strands of DNA by means of cyanine dyes.) More recently, they have been used for optical imaging of dye-labeled biomolecules, either in vivo or in vitro. (See, for example, U.S. Pat. No. 7,597,878.) Scientists favor using cyanine dyes in biological applications because, among other reasons, many of these dyes fluoresce in the near-infrared (NIR) region of the spectrum (600-1000 nm). This makes cyanine dyes less susceptible to interference from autofluorescence of biomolecules.
Other advantages of cyanine dyes include, for example: 1) cyanine dyes strongly absorb and fluoresce light; 2) many cyanine dyes do not rapidly bleach under a fluorescence microscope; 3) cyanine dye derivatives can be made that are effective coupling reagents; 4) many structures and synthetic procedures are available, and the class of dyes is versatile; and 5) cyanine dyes are relatively small (a typical molecular weight is about 1,000 daltons), so they do not cause appreciable steric interference in a way that might reduce the ability of a labeled biomolecule to reach its binding site or carry out its function.
Hydrocyanines and deuterocyanines are a reduced form of cyanine dyes. Because of the disrupted p-conjugation, they are essentially nonfluorescent molecules. In the presence of radicals, hydrocyanines or deuterocyanines oxidize back to the fluorescent cyanine dyes.
Hydrocyanine and deuterocyanine dye precursors are needed for use in labeling biomolecules as well as in vivo imaging for the diagnosis and prognosis of diseases such as cancer. Such compositions and methods are needed for aiding in the analysis of responses to various therapies. The present invention satisfies these and other needs.